Transmissions featuring floating transmission mainshaft gears such as associated with twin countershaft transmissions are well known and of which examples can be found in U.S. Pat. Nos. 3,237,472; 3,283,613; 3,425,290; and 3,885,446, the disclosures of which are incorporated herein by reference.
Such transmissions generally feature a plurality of floating mainshaft gears that encircle the mainshaft and are supported and driven by countershaft gears that are mounted on a pair of counter-shafts disposed on opposite sides of the mainshaft in substantial parallel spaced-apart relationship thereto.
The mainshaft gears are characteristically clutched to the mainshaft by means of a clutch mechanism that slides along external splines or flutes extending axially along the mainshaft and has radially outwardly extending teeth to engage internal teeth on the mainshaft gear so as to cause rotation of the mainshaft when the mainshaft gear being clutched thereto is rotatably driven. A problem long ago recognized has been the potential transfer of axial thrust between closely adjacent mainshaft gears when one of the mainshaft gears is being clutched to the mainshaft by a clutch mechanism moving axially toward both gears. In view of such, a variety of solutions have been devised over past years for the transmitting axial thrust imparted by an axially moving clutch to the mainshaft rather than to the gear adjacent the gear being clutched to the mainshaft.
Such solutions have generally been in the form of gear retainer(s) or thrust washers of one type or another that characteristically limit axial movement of the mainshaft gears to prevent them from engaging each other whether or not one of them is being clutched to the mainshaft.
One example of a retainer assembly for limiting axial movement of a transmission gear is disclosed in U.S. Pat. No. 2,397,905, the disclosure of which is incorporated herein by reference. Here however, a costly pivotal woodruff key is required to lock a thrust collar onto external splines of the mainshaft to prevent a gear from moving axially.
An example of a splined thrust washer for transmitting axial thrust from a gear set to a propeller drive shaft is disclosed in U.S. Pat. No. 3,894,621, the disclosure of which is incorporated herein by reference. Here, a splined thrust washer (52) is slid axially along the shaft splines to a transverse groove adjacent a stepped shoulder on the shaft and is held in place against the shoulder by splined collar (30). Thrust washer (52) is operative to transmit axial thrust of only one gear to the propeller shaft and, in addition to requiring the use of collar (30), also requires costly and complex machining of a stepped configuration to the propeller shaft exterior.
A more recent example of a transmission mainshaft gear retainer or thrust washer for preventing axial movement of two closely spaced gears to prevent transfer of axial thrust force therebetween is disclosed in U.S. Pat. No. 4,034,620, the disclosure of which is incorporated herein by reference. Here a thrust ring (104) is splined to the mainshaft between two adjacent gears and is held in place by means of snap rings (108, 110) on opposite sides thereof. The gears are further required to have costly and complex mating tongue and groove configurations that operate in conjunction with an additional snap ring (102) to limit movement of the gears away from each other.
An even more recent example of a particular arrangement of thrust washers that are secured to a splined transmission mainshaft by means of an elongate key is disclosed in copending application U.S. Ser. No. 329,134, filed Mar. 27, 1989, now U.S. Pat. No. 4,949,589, issued Aug. 21, 1990, assigned to the assignee of the present invention.
The instant invention addresses a problem presently existing with thrust washers that are provided with grooves in an annular surface surrounding an opening through which the mainshaft is received that, when in substantial alignment with corresponding axially extending grooves in the exterior surface of the mainshaft, define a keyway through at least one of which an elongate key is inserted to secure the thrust washer to the mainshaft but which heretofore has been provided with a cross-sectional configuration rendering it not only difficult to insert through the keyway but also providing the possibility of creating stress risers in the corners of the grooves when improperly inserted therethrough.